Systematic investigation of the magnetic field and temperature dependence of the helical length and skyrmion distances in Cu₂OSeO₃

Skyrmions are topologically stable particle-like objects comparable to spin vortices at the nanometre scale. They consist of about 10-100 nm large spin rotations. Remarkably their spin winding number is quantized making them extremely robust objects. Once formed they order in a 2-dimensional, typically hexagonal superstructure perpendicular to an applied external magnetic field. Their dynamics have links to flux line vortices as in high temperature superconductors. Cu₂OSeO₃ is a unique case of a multiferroic materials where the skyrmion dynamics can be controlled through the application of an external electric field. This non-dissipative method offers technological benefits for example in low-energy, high density data storage devices or for quantum computation. Important for technological applications would be a stability range of the skyrmion phase up to room temperature. While room temperature skyrmion materials exist, Cu₂OSeO₃ orders magnetically slightly below 60 K. Our combined small angle neutron scattering and SQUID magnetization measurements did provide direct evidence that the stability range of the skyrmion phase can be extended in Te-doped Cu₂OSeO₃. Neutron scattering also provides the full information about the orientation and the skyrmion distances. Our data provide new aspects about the systematic changes of the helical length and skyrmion distances with temperature and magnetic field. This was measured throughout the entire H-T phase diagram. In addition, various crystal orientations and magnetic field histories were applied where even metastable skyrmions were generated. This did provide remarkable changes in the H-T skyrmion stability range and skyrmion distances. Our results offer new valuable information about the parameters in the spin Hamiltonian, which are responsible for the formation of these fascinating quantum protected objects.

Reference: J. Sauceda Flores, et al., arXiv:2303.02653